Aquaculture is the farming of organisms in an aquatic environment. Until the 1970s, aquaculture was not a significant contributor to the global market for seafood. However, in the last 40 years global aquaculture has expanded from an estimated 3.5 million tonnes in 1970 to about 66.7 million tonnes in 2006. Further, government restrictions to preserve populations of certain native species have increased the demand for seafood produced in controlled artificial environments such as in aquaculture ponds. The production of catfish in catfish farms is one example of the growing, large-scale aquaculture industry. Other species produced by the aquaculture industry include crayfish, oysters, shrimp, Tilapia and Striped Bass.
According to the Food and Agriculture Organization of the United Nations (FAO) Fisheries and Aquaculture Department, it is estimated that by 2012 more than 50 percent of global food fish consumption will originate from aquaculture. With aquaculture now making up a significant portion of total seafood supply, the increased production from aquaculture has also led to significant environmental impact and competition for diminishing natural resources from other sectors such as agriculture. In particular, pond production continues to dominate aquaculture production and is especially vulnerable to water scarcity. Aquaculturists have thus been under pressure to intensify production and grow more seafood with less water and land.
As aquaculture production intensified over time, providing enough oxygen in the pond environment also became a major challenge. If not enough oxygen is supplied, anaerobic conditions may appear and toxic gas production (hydrogen sulfide, ammonia) increase, affecting shrimp health and, thus, leading to disease outbreak. In the early days pond production was limited to the biomass that could be sustained with only natural weather-driven re-aeration. Over the years, first emergency aeration, then routine nightly aeration and finally 24-hour aeration was added, which is now standard practice in the industry.
However, 24-hour aeration is expensive especially in areas with limited access to electricity and/or fuel. As a general comparison, in important shrimp farming countries such as Thailand, India or Ecuador, existing aquaculture methods achieve a stocking density of 200, 100 and 30 postlarvae per square meter, respectively.
Further, even if oxygen needs are met, concentrations of nitrogenous compounds from waste decomposition often reach limiting or toxic levels. The aquatic environment may also comprise other organisms apart from the farmed organisms, such as plankton, algae and bacteria. Pathogenic or undesirable organisms may affect the growth, health and quality of the farmed species. Problems such as algal “blooms and crashes” may also be experienced at high production rates, discouraging high stocking densities. For example, a rapid growth or accumulation in the populations of unwanted algal species in the aquaculture pond, in particular blue green algae, can result in a undesirable “off flavor”, causing the flesh of the fish to have an unacceptable taste and odor.
According to the FAO, China, Thailand, Viet Nam, Indonesia and India dominate the global production of shrimp and prawns. Shrimp farms may be categorized as open systems and closed systems.
Open system shrimp farms are generally open to the environment, such as open-air ponds constructed near oceans to contain and grow shrimp. These open shrimp farms suffer from vagaries of predators, the weather, diseases and environmental pollution. Saltwater from the ocean must be continually circulated through the ponds and back to the ocean to maintain adequate water chemistry for the shrimp to grow. The shrimp farmers must supply daily additions of dry food pellets to the shrimp as they grow.
Closed shrimp farms are generally self-contained aquaculture systems. While closed shrimp farms have greater control over the artificial environment contained therein, they have not been entirely satisfactory because of limited production rates, water filtration and treatment problems, and manufactured feed. Although some of these shortcomings can be overcome by increased capital expenditures, such as for water treatment facilities, the increased capital, labor and energy costs may be prohibitive.
Accordingly, there still is a need in this technical field for improved aquaculture methods, in particular methods that increase the production intensity by providing increased oxygen levels and reduced levels of nitrogenous compounds in the pond environment.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate on exemplary technology area where some embodiments described herein may be practiced.